This invention relates to an apparatus and method for testing the reflectivity and transmission of light by various materials or objects and, more particularly, to the testing of the total light reflectivity and total light transmission of optical elements, and especially those intended for use by humans such as rearview mirrors for vehicles and the like.
In the manufacture of optical elements such as rear view mirrors and the like, it is preferable to test each mirror element to determine its optical qualities, namely, the amounts of an incident light beam it reflects and transmits. Various apparatuses and methods are known for conducting such testing. In one method, a light source provides a single beam of light which is split into a pair of identical light beams which are directed through separate test apparatus each of which includes either a standard or known sample or a test sample of a mirror or the like. Not only is such duplication of test apparatus expensive and often subject to error, but most such apparatuses require separate testing of reflectivity and transmission of light through the samples. Consequently, it is often difficult to assure that the same area of the test piece is being tested for reflectivity and transmission.
In other apparatuses, a standard sample and a test sample are tested alternately, one after the other by mounting them in appropriate holders and inserting them in a test apparatus. In such structures, it is usually necessary to test the standard sample immediately before or immediately after the test sample in order to determine an accurate and representation reading. Moreover, such structures have been subject to inaccuracies and have generally been quite complex. They also have required the separate testing of each sample for light reflectivity or transmission or the modification of the apparatus to obtain the separate values.
An additional problem with certain prior reflectivity and transmission testing methods has been the necessity of measuring either specular or diffuse reflection separately. The two types of reflection must then be added by electronic means or the like to obtain a proper readout. Further, it has often been difficult to obtain an indication of reflectivity and transmission equivalent to that of the photopic human eye response.
In the mass production of optical elements such as rear view mirrors for automobiles, the prior known structures and methods mentioned above have caused significant problems and delays in testing each optical element produced. A substantial need has therefore existed for a light reflectivity and transmission testing instrument or apparatus and method which enables the simultaneous testing of the total reflectivity, including both specular and diffuse reflection, as well as the total transmission of light of the identical area of an optical element in a manner similar to the response of the photopic human eye. A need has also existed for the capability of such testing on a successive, high production basis without having to modify the test apparatus to determine the desired, distinct values or to insert a standard test sample after each production sample is tested.